Percutaneous transluminal angioplasty ("PTA") and percutaneous transluminal coronary angioplasty ("PTCA"), wherein a dilation balloon is advanced through the vascular system to a stenosis and inflated to open the blockage, is now a commonplace procedure. In about one-third of the cases, however, after the procedure restenosis can occur and that can require another dilation procedure. It is estimated that the total cost of restenosis requiring an additional dilation procedure or some other treatment, is over 2 billion dollars per year worldwide.
Various agents that may reduce restenosis can be applied to the dilation site. For example, antithrombolytic agents such as heparin may prevent clotting. Antiproliferative agents, such as dexamethasone, can prevent smooth muscle cell migration and proliferation.
Various methods have been proposed to effectively deliver such agents to the dilation site. For example, in U.S. Pat. No. 5,087,244, to Wolinsky, a catheter is disclosed having a thin walled flexible balloon with a plurality of small holes. After an angloplastic procedure, such a balloon can be advanced to the dilation site and inflated with heparin, or some other medication. The medication exits the inflated balloon, which is in contact with the arterial wall, through the holes. Such "weeping" balloons may damage the arterial wall, however. In addition, having to insert a second catheter for drug delivery after removal of the dilation catheter is cumbersome and time consuming. It can also be difficult to precisely locate the dilation site after the dilation catheter is removed.
It is, therefore, advantageous to provide a catheter which can both dilate the stenosis and immediately thereafter deliver drugs directly to the dilation site. U.S. Pat. Nos. 4,824,436 and 4,636,195, also to Wolinsky, disclose a catheter with a dilation balloon and a pair of occlusion balloons proximal and distal to the dilation balloon. A drug delivery conduit is provided between the distal occlusion balloon and the dilation balloon. After dilation of the stenosis, the dilation balloon is deflated, the occlusion balloons are inflated and a drug is delivered. Because of the presence of the dilation balloon, there is only a small region available for drug delivery. Drug delivery may, therefore, be slow and of too low volume to be effective.